Found this is a glossary of submariners’ slang. It’s not one of the slang terms to my eyes, oddly, so I don’t know why it’s listed. Maybe “1MC” means something special (I don’t know what it means slang or not).
Diver’s 1MC Announcement - “There are divers over the side, do not rotate screws, cycle rudders, take suction from or discharge to the sea, blow flood or vent any tanks, or operate any underwater equipment or activate sonar. There are divers over the side.”
Also, “over the side” sounds weird to me, but what the hey.
Also, do these phrases ring bells for the local bubbleheads?
1MC is the public address system on the sub - making an announcement over the 1MC means everybody gets the message (which is what you want for a safety announcement, of course) 1 Main Circuit - Wikipedia
OP ETA: I guess I didn’t add, to be clear: all the other activities in the operation, care, and feeding of the sub as being hazardous to a diver I can see. But with the sonar: is some sort of device deployed?
Otherwise I have this image of some colossally loud sound impinging on the diver with harmful effects, and that sounds unlikely…
No, that’s exactly it. Active sonar is very loud (over 230 dB) when generated, and water transmits sound much better than air. So a sonar ping a few feet away could easily deafen a diver.
Various green groups have been / still are up in arms that active sonar is essentially torturing the whales and other sea creatures. A quick Google for [sonar whale harm] will bring up a variety of sites and cites of varying believability. But you’ll also find news articles about various real Federal court cases that went against the real US Navy and now limit their use of some active sonar devices.
If there was a diver in the water when an active sonar was fired (though I am not sure about a submarine’s sonar) the intensity would be enough to kill the diver. A strong bi-static sonar (see the 230 dB) is quite loud enough to kill at close range.
How does a submarine generate such a loud sound? I would guess that it would be generated from some kind of speaker using electrical power to convert an electronic signal into sound, and not, say, a big bell that they clang back and forth underwater, but I have no idea if my guess is at all accurate.
The BQQ-5 (what I worked on back when) could put 196KW of acoustic energy into the water. But, since Submarines rarely, if ever, light off the main suite in active mode (only happened twice in my 6 years, and then only when entering port) the diver warning applies mainly to underwater comms and fathometers, both of which can injure divers close aboard.
I worked for a large science/engineering company once (though our branch was rather small).
We called in an expert for something or another (or maybe he was just passing through…I forget).
Anyway, for his age his health was pretty bad apparently.
The story I got was that he and another guy were working on a ship’s radar system. ANOTHER large vessel came into port with their radar working. Well, these guys were basically at the focus of the non radar active array.
Military aircraft with which I’m familiar incorporate a “weight on wheels” sensor that forbids the plane’s radar from emitting when it’s on the ground - because it can be lethal to nearby people.
On modern fighters, the minimum safe distance (in the direction of the main lobe) in the hundreds of meters, I seem to recall.
Wow.
I can see how that might happen-another example of why some of those stupid rules (which in this case came one accident too late) aren’t so stupid after all.
